Composite pavement and method oe pboducino same



July 8, 1924. 1,500,451 w. 5. HACKER COMPOSITE PAVEMENT AND METHOD OFPRODUCING S AME Filed Nov. 26, 1920 INVENTOR.

ATTORNEY Patented July 8, i924.

WILLIAM E. HACKER, OF LOS ANGELES, CALIFORNIA.

COMPOSITE PAVEMENT AND METHOD OF PRODUCING SAHE.

- Application filed November 26, 1920. Serial No. 426,439.

To all whom it may concern:

Be it known that I, WILLIAM E. HACKER, a citizen of the United States,residing at Los Angeles, in the county of Los Angeles and State ofCalifornia, have invented new and useful Improvements in CompositePavements and Methods of Producing Same,

of which the following is a specification.

' in bitumen as to effectually seal it against entrance of moisture, andof such plasticity and toughness that it will effectually protect thelargerparticles of mineral matter forming the main body of the avementfrom the wear and abrasion of tra c.

The pavements which have come the nearest to \having all of thesecharacteristics have been those of the bituminous concrete type composedof a well graded mineral aggregate consisting of particles of crushedstone, gravel or slag varying from a maximum size, havin a' diameter ofapproximately one-half t e depth of the completed wearing surfacesection to an extremely fine powder, the several sizes being combined insuch amounts as to make a mineral aggregate of maximum density or onecontaining a minimum'of voids, this mineral aggregatebeing combined withsuflicient bituminous cement to coat all the particles of aggregate andfill the few remaining voids, the mixture being then spread andcompressed upon a suitable foundation.

A pavement mixture made by this method is not only dense but also isrelatively stable under traffic due to the interlocking of the largestsized particles of mineral aggregate with the intermediate sizedparticles. However, it was found necessary to waterproof the uppersurface of thepavement by applying hot bituminous cement in a thin layerand rolling into same either sand or fine stone chips forming what isknown as a flushcoat mat or finish. It was then found that as soon asthis flushcoat mat was worn off by trafiic, the upper faces of thelarger stones exposed to. traflic, soon became shattered or abraded alsothat water was not only absorbed by such stones, but also worked its wayinto the mixture, around the sides of such stones causing early ravelingand disintegration of the mixture under traflic.

It was, therefore, necessary in the practical, commercial, laying ofsuch avements, to increase the proportion of the t ier aggregate ormortar element to such an' extent,

that during the rolling of the hot mixture at time of laying, also whenunder traflic in hot weather, this excess of mortar would be forced bysuch pressure to the surface and,

to a certain extent at least, protect the larger sized particles ofaggregate. Natur ll however, only a small portion ofsuch e cessmortarwould find its way to the immediate surface of the pavement. Thereforean excessive amount of such mortar remained in the body and lowerportion of the pavement section, holding the larger particles ofaggregate apart and thus reducing the stability of the pavement due tomore or less preventing the interlocking of'the particles of aggregate.In other words, it became a matter of individual judgment in theconstruction of each street to what extent stability should besacrificed to obtain resistance to abrasion and entrance, of moistureand vice versa.

This compromise was necessary, due to the structure of the wearingsection, the structure being homogeneous and of uniform physicalcharacteristics throughout its entire depth. a

The resent invention overcomes this difficulty by producing a structurewhich is not homogeneous throughout its depth, but, on the contrary,isrelatively plastic at its immediate upper surface and fora slightdepth below the surface, the remainder of the body of the pavement beingrelatively so stable as to prevent displacement of the structure or anyportion thereof under traffic.

In the practical construction of bituminous concrete pavements theabove-mentioned defects have been recognized, but as the commercial lossdue to raveling and disintegration of mixture caused by abrasion and.entrance of moisture from above has been greater than from any othercause,

coarse aggregate bituminous concrete mixture and before same has becomethoroughly compacted or chilled there was superposed thereon a fineaggregate bituminous mortar mixture, rich in bituminous content, the twodissimilar mixtures being rolled, blending the upper fine aggregatemixture with the upper portion of the coarser bituminous concretemixture. This combination accomplished its object of waterproofing ofsurface and also protected the surfaces of the uppermost coarseparticles of the bitumi-' nous concrete mixture from abrasion bytraific. However, the practice in such cases did not increase thestability of the pavement structure as a whole and under present daymodern trafiic conditions an increase of stability is not onlydesirable, but an extremely important essential.

The object of the present invention is to produce a product combiningnot only all of the advantages of the pavements de-. scribed above, butalso one possessing this desirable greater stability. The manner inwhich this greater stability is obtained is by using for the lowerportion of the pavement, a bituminous concrete mixture preferablycomposed of particles of aggregate varying in sizefrom those whosediameter is approximately one-half of the depth of the wearing surfacesection to fine dust which will pass a screen having 200 meshes perlineal inch. The amounts of each size used may be predetermined or not,and preferably are such as to produce a mineral aggregate having notmore than 18% of voids. Y I have found that it is possible, by the useof a plastic, bituminous mortar upper portion, to obtain greaterstability in a bituminous concrete pavement than has been obtainableunder former practice, above referred to.

The manner in which I produce the structure, possessing the abovedesired characteristics is by:

(a) Laying a coarse aggregate bituminous concrete mixture soproportioned as to contain less fine aggregate and less bituminouscement than would be permissible if this bituminous concrete mixtureformed a complete pavement wearing section, that is, by using a mineralaggregate having a relatively small percentage of voids, using acomparatively small proportion of fines, and using an amount of bitumenand fines combined not more than substantially that amount required tofill the spaces otherwise existing between the coarser particles, andthus producing a structure possessing the essential stability.

(6) Superposing upon the above described bituminous concrete mixture afine aggregate bituminous mortar. richer in bituminous content thanwould be permissible if this bituminous mortar should form the Forconvenience in describing the product of my invention and the method ofproducing said product I submit the accom panying diagram, in which theportion let tered A represents a foundation which may be of any type offoundation or base either natural or prepared, preferably of a plasticrather than of a rigid character and which is of suflicient structuralstrength to support the weight of trafiic to which the pavement may besubjected.

The portion lettered B represents a dense stable bituminous concretemixture and the portion lettered a relatively fine aggregate mortarmixture, rich in bi tuminous content.

. The portion lettered D represents the portion intervening betweenportions B and C formed b the mixture C pressing into mixture thusforming the serrated, non-cleavage line hereinafter and moreparticularly described.

The bituminous concrete mixture consists of particles of mineralaggregate of various sizes mixed preferably hot with hot bituminouscement of appropriate consistency. The mineral aggregate may consist ofcrushed rock, crushed or uncrushed gravel or slag or any other suitableequivalent material. The bituminous cement/may beprodueed from asphalticor coal tar materials.-

I first spread this bituminous concrete mixture B upon the foundation Ain a loose layer of uniform depth approximately equal to the desireddepth of the completed pavement section.

I then spread the rich bituminous motor mixture G in a comparativelythin layer, over the bituminous concrete mixture B and then compact thewhole structure by rolling, tamping or other suitable means ofcompression, so that the resulting product consists of a bituminousconcrete mixture of great denseness and stability with its upper surfacesealed by the plastic and relatively unstable fine aggregate mortarmixture.

In producing .the coarse aggregate bituminous concrete mixture B, Iprefer to use a mineral aggregate consisting of particles varying insize from those whose diameter is approximately one-half the depth ofthe wearing surface section to fine dust Per cent. Passing a screenopening of not more than of the depth of completed pavement and retainedon 1}" round opening screen 40-70 Passing 1} round opening screen, re-

. tained on a #4 mesh sieve 10-25 Passing #4 mesh retained on #10 meshsieve 5-15 Passing mesh sieve -28 The amount of the aggregate which willI pass a #10 mesh sieve shall preferably be within the above statedlimits and preferably be that amount which will reduce the voids in thetotal aggregate to less than 18% of its total volume.

The amount of bituminous cement used will naturally vary with the purityof the bituminous cement used and with the fineness and surface area ofthe mineral aggregate used and shall be sufficient to coat all theparticles of mineral aggregate and pro:

duce a mixture containing from 4 to 8% by weight of bitumen soluble incold carbon bisulphide.

The fine aggregate mixture shown as layer C in the diagram, shallconsist of either sand, fine crushed rock, crushed or uncrushed gravel,slag or equivalent mineral matter, all of which will pass a. #4 mesh orfiner sieve mixed preferably while hot with hot bituminuous cement ofappropriate consistency, prepared from asphalt or coal tar materials, insuch proportions that the resulting mixture will preferably contain from8 to 17% of the customary methods, the coarse aggregate mixture isspread on the grade or foundation by means of shovels or forks, andrakes or other appropriate .means in a layer of uniform thicknessapproximately. equal to the desired depth of the completed wearingsurface section. Before this mixture has become too much chilled, orfull compacted, the fine aggregate mixture is spread in a comparativelythin layer over the coarse mixture B and the two layers compacted byrolling, tamping or equivalent means of compression.

While I prefer to spread the fine mixture C over the coarse mixture Bbefore the coarse mixture B has received compression, this is not anessential point in the invention and if desired, the lower coarsemixture may be given partial compression by rolling if the fine mixtureis applied at such a time and in such a-manner that the subsequentrolling of the two mixtures together will not only bind the two mixturestogether, but will also, due to the kneading action of the roller,disturb the lower coarse aggregate to such an extent that the upper fineaggregate mixture is forced down into and between the uppermost stonesin the coarse aggregate mixture blending the two mixtures, so that,after the completed wearing surface section has received ultimatecompression, there shall not be a distinct plane of cleavage between thetwo mixtures,

ut on the other hand, a vertical sawed section ofthe completed wearingsurface shall show, if anything, a serrated line at the upper surfacesof the uppermost coarse stones in the lower mixture.

By using the proportions of ingredients, and by following the methodsdescribed above,'thus locating the different sizes of mineral aggregatein their proper places, the resulting. product consists of a monolithicbituminous structure, the body of which consists of a bituminousconcrete of great denseness and stability with its upper surfaceprotected by the plastic and relatively unstable bituminous mortar.

The relative quantities of each of the two bituminous mixtures,'used,may and should be varied in accordance with the physical characteristicsof the materials used for the coarse aggregate in the body or lowerportion of the pavement wearing section, as obviously a thicker layer ofthe fine aggregate surface mixture is advisable, to protect a \coarseaggregate composed of soft or brittle mineral matter, than is requiredto protect a coarse aggregate composed of hard and tough stone, gravel,etc.

Under the ordinary conditions three (3) to five (5) parts by volume ofthe bituminous concrete mixture and one 1) part by volume of thebituminous mortar will give the best results.

It will be seen from the above description that the bituminous concretemixture used for the lower portions or body of the pavement is one inwhich the various sized particles of aggregate are so proportioned inamount, that'if such a mixture were spread on a firm foundation andthoroughly compressedby rolling with a heavy'road roller or otherequivalent means, theresult' would be an exceedingly dense stable bituminous concrete, the upper surface of which would be relatively smooth,yet present a mosaic appearance, showing particles of coarse aggregatebound together by, but not materially protruding above the fineaggregate content of the bituminous concrete which has been forced up tothe surface by the compression of the roller.

However, when the bituminous concrete mixture is spread loose by rakingas described above, a large number of the larger sized particles ofaggregate protrude above the mass of the mixture, and if the bituminousmortar mixture "is spread thereon before such protruding particles havebeen completely forced down into the body of the structure andcompression is then applied ]by rolling or other means, the result will(a) Some of the bituminous mortar mixture will be forced into any andall spaces between the tops of suchvparticles as protruded above themass of the bituminous concrete mixture.

(6) Some of the bituminous mortar mixture. will be compacted into arelatively thin layer above .the .tops of the uppermost particles ofbituminous @-concrete mixture.

(0) Many vof "the uppermost particles of the bituminous concrete mixturewill be embedded partially in "the finer portion of the coarse aggregatebituminous concrete mixture, and partiallyembedded in the fine aggregatebituminous mortar surface mixture, thus firmly jointing or interlockingby blending of the two mixtures together.

I have, of course, specifically disclosed the best practical embodimentof my invention I of which I am cognizant, but it is obvious that in'thefuture practice of the invention departure from the scope such changesmay be made as do not involve of my invention as claimed. I

I claim: v 1. A unitary bituminous pavement wearing structure composedof two dissimilar bituminous mixtures, the lower being a relatively'stable coarse aggregate bituminous concrete containing relatively'coarseand relatively fine mineral bodies and containing not more thansubstantially that proportion of relatively fine mineral bodies andbitumen which will fill the spaces otherwise existing between therelatively coarse bodies if compacted alone, the upper mixture being arelatively plastic fine aggregate bituminous mortar containingrelatively fine' mineral bodies and containing not less thansubstantially that proportion of bitumen which will fill the spacesotherwise existing between the mineral bodies if compacted alone, thecontiguous portions of the two mixtures being mo auf plastic fineaggregate bituminous mixture 7 containing relatively fine mineral bodiesand containing not less than substantiallythat proportion of bitumenwhich will fill the spaces otherwise existing between the mineralbodiesif compacted alone, and compacting the pavement by compression appliedto the upper course and thereby forcing the contiguous )ortions of thetwo courses into blending at mixture with each other to produce aunitary mass.

. 3. A bituminous pavement wearing structure composed of two bituminousmixtures of dissimilar physical characteristics, to-wit: (a.) arelatively stable bituminous concrete mixture consisting of bitumen fourto eight percent by weight and a mineral aggregate composed ofparticlesvarying in size from 'those whose diameter is not more thanseventenths of the depth of the completed pavement structure, to thosewhich will pass approximately, a 200 mesh sieve, theamounts of theseveral sizes used beingsuch-fthat the voids in the-mineral aggregate ofthis mix,- ture, considered by itself, are not more than eighteenpercent of the volume of themineral aggregate, the weight of suchaggregate which will ass a ten mesh sieve being not less than fteenpercent nor more than twenty eight percent of the weight of the totalmineral aggregate used "in this mixture; and I(b.) a relatively plasticbituminous mortar mixture, composed of eighty three percent to ninetytwo lpercent by weight of mineral aggregate, al of which will pass a'sieve having four meshes per linealinch and eight percent to seventeenpercent by weight of bitumen; said bituminous mortar mixture beingsuperposed upon the bituminous concrete mixture and compressed and thecontiguous portions of the two mixtures being thereby blended to producea unitary mass.

4. A bituminous pavement wearing structure composed of two dissimilarsuperposed bituminous mixtures, the lower being a relatively stablecoarse aggregate bituminous concrete mixture, the mineral aggregate ofwhich contains not more than approximately eighteen percent of voids byvolume, the particlesof the aggregate being coated with cent toseventeen percent of bitumen i liyweight, the contiguous portions of themixtures being so bonded and blended together by compression. as toproduce a unitary mass.

5. A bituminous pavement wearing structure composed of two dissimilarbituminous mixtures, the first being a relatively stable coarseaggregatebituminous concrete 'xture the graded mineral aggregate of W chcontains not more than approximately eighteen percent of voids byvolume, and the amount of such mineral aggregate that will pass a tenmesh screen being not more than approximately twenty-eight percent byweight, the particles of the aggregate being coated with bitumen in anamount approximatel four to eight percent'by weight, the second beingarelatively plastic fine aggregate bituminous mortar containingapproximately eight percent to seventeen percent of bitumen by weight,the two contiguous portions of the mixtures being so bonded and blendedtogether by compression as. to produce a unitary mass,

6. A bituminous pavement wearing structure of the kind specified inclaim 4, characterized further by the coarse aggregate bituminousconcrete mixture being such that if a given volume of said mixtureshould be compacted by itself, the specific gravity of said compactedmixture would equal at least ninety percent of the specific gravity ofthe mineral aggregate used in said mixture.

7. The combination, in a bituminous pave- I ment wearing structure of, abituminous concrete mixture, the mineral aggregate 'of which containseighteen'percent or less of voids containing bitumen in an amountapproximately four, percent to eightpercent by weights spread in a layerof substantially uniform thickness upon which layer is. spread acomparatively thin layerof a relatively rich-bituminous mortar mixturecontaining bitumen approximately eight to seventeen percent by weightthe whole being compacted and the contiguous portions of the twomixtures blended together by compression. I 8. A bituminouspavement'wearmg structure com osed of two bituminous mixtures ofdissimilar physical characteristics, towit:

(a arelatively stable bituminous concrete mixture consisting of mineralaggregate and bituminouscement comin within the following proportions byweig t:

' Per cent. Coarse aggregate which will passa screen having openings notlarger thanf of the depth of the completed wearing structure. and whichwill be retained on 1} inch round opening screen 407O Intermediate sizeaggregate which will pass e; inch round opening screen and be retainedon a #10 mesh sieve 15-40 Fine'aggregate which will pass a #10 meshsieve 15-28 Bituminous cement, sufficient to coat all par-- ticles ofthe aggregate and produce a mixture containing 48 per cent of bitumensoluble in cold carbon bisulphide; and (b) 'a relatively plastic.bituminous mortar mixture composed of eighty three per cent to ninetytwoper cent by Wei ht of mineral aggregate, all of whlch wil pass a sievehaving four meshes per lineal inch, mixed 'wit eight per cent toseventeen per cent by weight of bitumen, this latter bituminous v mortarmixture being superposed upon the previously spread bituminous concretemixture and compressed so as to produce a bummmous pavement structureconsistmg of a uniformly graded, dense, stable bituminous;

concrete mixture throughout the lower two thirds to three fourths of itsdepth and of a rich, plastic, bituminous mortar in the u permost onefourth to one eighth of its depth, the intervening portion beingcomposed of large particles of the lower portion of the structure boundtogether .partly by some of the fine bituminous coated aggregate fromthe lower portion of the structure and partly by some of the plasticflexible bituminous mortar forming the surface of the pavement, thusforming a structure in which the two abovedescribed mixtures are soblended that a vertical cross section of the completed structure willnot show a distinct plane of cleavage between the two mixtures.

Signed at Los Angeles, California, this 16th day of November, 1920;

, WILLIAM E. HACKER. Witnesses:

L. BELLE WEAVER, Fnnonmo'x S. LYON.

